Treatment of recycled kraft pulps with Trichoderma reesei hemicellulases and cellulases

Effects of recycling ECF-bleached softwood kraft pulp on pulp properties we re evaluated in the laboratory. The tensile strength, fiber flexibility and WRV lost during drying of the pulp were recovered by refining between the cycles which, however, resulted in deteriorated drainage properties. The re cycled pulps were treated with purified Trichoderma reesci cellulases and h emicellulases and the changes in fiber properties due to enzymatic treatmen ts were characterized. The endoglucanases (EG I and EG II) significantly im proved pulp drainage already at low dosage levels, and EG II was found to b e more effective at a given level of carbohydrate solubilization. Combining hemicellulases with the endoglucanase treatments increased the positive ef fects of the endoglucanases on pulp drainage. However, as a result of the e ndoglucanase treatments a slight loss in strength was observed. Combining m annanase with endoglucanase treatments appeared to increase this negative e ffect, whereas the impact of xylanase was not significant. Although the dra inage properties of the pulps could be improved by selected enzymes, the wa ter retention capacity of the dried hornified fibers could not be recovered by any of the enzymes tested. (C) 2000 Elsevier Science B.V. All rights re served.